Purpose: The purpose of the paper is to review the characteristics of systems that combine P2P technology with explicit ontologies and assess the benefits of these technologies for inter-organizational knowledge management. Design/methodology/approach: We characterize existing technologies with respect to a number of aspects that are relevant to knowledge management on a technical level. We further provide an example of an existing system and categorize it according to the aspects. Findings: We conclude that ontology-based P2P systems are in general beneficial for distributed knowledge management systems and that the design of such systems can be guided using the aspects we distinguish. Originality/value: The paper presents the first attempt to rigorously identify and discuss the design space of ontology-based P2P systems.